1. Field of the Invention
The present invention relates to a semiconductor module, and in particular, to a semiconductor module with a radiator.
2. Description of the Related Art
Portable electronics devices, such as mobile phones, personal digital assistants (PDAs), digital video cameras (DVCs), and digital still cameras (DSCs) have become increasingly sophisticated. A further reduction in size and weight is, however, necessary for such devices to continue to succeed in the market, and as such, these devices now require highly integrated system LSI chips. User-friendliness and convenience is required for these devices as well, resulting in an increased need for highly functional high performance LSI chips. Although the highly integrated LSI chips require a large number of input/output ports, there is a strong desire to reduce their package size. To meet these conflicting requirements, the development of a semiconductor package suitable for high density board packaging of semiconductor parts is strongly desired. In response to such needs, a variety of packaging technologies, called chip size package (CSP) technologies, have been developed.
A CSP is formed in such a way that a semiconductor wafer (semiconductor substrate), in which LSI chips (circuit elements) and external connecting terminals connected to each LSI chip are formed on one principal surface thereof, is diced into individual chips. Accordingly, the CSP, which is substantially the same size as an LSI chip, is fixed on a mounting board, resulting in a reduction in the size of the mounting board on which the CSP is mounted. Therefore, the use of the CSP in a system allows the overall size of that system, such as an electronics device, to be reduced.
Moreover, power consumption of LSI chips is increasing every year with the associated increase in performance and functionality. This leads to an increase in the power consumption per unit volume (heat density) of a CSP (semiconductor module) with an LSI chip, resulting in a greater need for radiation of the extra heat away from the CSP. One proposed approach to this issue is a method for effectively radiating out heat generated in the CSP (semiconductor module) through a film which is formed on the rear surface of a semiconductor substrate, which is a component of the CSP (semiconductor module). Such a film is a heat radiative film with a high thermal emissivity, e.g., a film containing ceramic powder, or a heat conductive film with a high thermal conductivity, e.g., copper or aluminum.
In general, a radiator, and especially a heat conductive film, used in the CSP (semiconductor module) is subjected to internal stress in the extending direction of the radiator during the process of formation. The internal stress is retained in the radiator of each individual CSP after formation. This stress causes the radiator to be separated from the semiconductor substrate, resulting in reduced reliability of the CSP (semiconductor module). In particular, there is a high possibility of separation of the radiator from the semiconductor substrate when the CSP (semiconductor module) is heated.
If the development of a thinner semiconductor substrate progresses in the future facilitating a reduction in the thickness of the CSP (semiconductor module), the remaining internal stress in the radiator will have a significant relative impact on the thinned semiconductor substrate. Accordingly, for example, the remaining internal stress in the radiator greater than the stiffness of the semiconductor substrate may cause the CSP (semiconductor module) together with the semiconductor substrate to change shape and thus to warp, even if there is no separation of the radiator from the semiconductor substrate.